The invention relates to internal combustion engine carburettors of the kind which comprise, in an intake manifold, a throttling member carried by a rotary shaft and connected to an accelerator control which enables the driver to open such member against the force of resilient return means which act on such shaft and tend to return the throttling member into a minimum opening position corresponding to engine idling.
Such resilient return means have been formed by a single spring which is subjected to a deforming force when the driver opens the throttling member. Safety requirements now lay down that at least two separate return springs must be provided each of which is able to return the throttling member to its idling position. The simplest method would consist in disposing the two springs in parallel, but this would result in practice in doubling the force which the driver must exert to open the throttling member, since each spring must exert force adequate to enable it to reclose the throttling member on its own -- i.e., if the other spring breaks.
It is an object of the invention to provide such return means using two springs without however appreciably increasing the force required to open the throttling member and without substantially increasing the complexity of the construction.
To this end, the resilient return means of a carburettor comprises a member rotatable about the shaft carrying the usual throttle member or butterfly valve and two return springs. The first spring is tensioned between said member and the carburettor frame for exerting on said member a force urging it angularly in the direction of closure of said throttle member. Cooperating abutment means on said shaft assembly and member limit the extent of angular movement of said member and shaft under the action of said first spring. The second spring is compressed against said member and exerts a torque tending to rotate it in a direction opposite to that due to said first spring and lower than the torque of said first spring. Last, there is provided stationary abutment means for limiting the extent of movement of said member under the action of said second spring upon failure of said first spring.
The invention will be better understood from the following description with reference to the accompanying drawings, such description and drawings relating to a preferred embodiment.